CVE-2026-43966
LOWDescription
Improper Neutralization of CRLF Sequences in HTTP Headers ('HTTP Request/Response Splitting') vulnerability in ninenines cowlib allows HTTP response splitting via non-VCHAR bytes in structured-fields string values. cow_http_struct_hd:escape_string/2 in cowlib only escapes \ and ", passing all other bytes through verbatim. This creates an encoder/decoder asymmetry: the matching parser accepts only printable ASCII (0x20–0x7E, excluding " and \), but the encoder emits any byte including CR and LF. An application that builds a structured HTTP header via cow_http_struct_hd:item/1 (or a higher-level wrapper such as cow_http_hd:wt_protocol/1) from attacker-controlled input can have \r\n injected into the serialized header value. Once on the wire, the injected CRLF terminates the current header and any following bytes are interpreted as a new header, enabling HTTP response splitting. This issue affects cowlib from 2.9.0.
How to fix
No published remediation has been found for this vulnerability's affected products yet.
Mitigation guidance may be in the linked vendor advisories in the References section below.
TridentStack Control tracks known vulnerabilities across your Windows, macOS, and Linux fleet and shows the fix as soon as one is published. See how it works
CVSS v4 Vector
Exploitability
Impact
CVSS:4.0/AV:N/AC:L/AT:P/PR:N/UI:N/VC:N/VI:N/VA:N/SC:N/SI:L/SA:N/E:X/CR:X/IR:X/AR:X/MAV:X/MAC:X/MAT:X/MPR:X/MUI:X/MVC:X/MVI:X/MVA:X/MSC:X/MSI:X/MSA:X/S:X/AU:X/R:X/V:X/RE:X/U:X
Exploit Intelligence
Low risk: more likely to be exploited than 24% of all known CVEs.
References
Related Vulnerabilities
Other CWE-113 vulnerabilities, ordered by exploit likelihood. View all
| CVE | Severity | CVSS | EPSS | Exploited | Fix |
|---|---|---|---|---|---|
| CVE-2022-37436 | Medium | 5.3 | 58% | - | Fix |
| CVE-2024-52875 | High | 8.8 | 30% | - | - |
| CVE-2016-5699 | Medium | 6.1 | 10% | - | Fix |
| CVE-2016-8024 | High | 8.1 | 8.7% | - | - |
| CVE-2017-17742 | Medium | 5.3 | 5.6% | - | Fix |
| CVE-2016-5325 | Medium | 6.1 | 4.1% | - | Fix |
Common questions
How do I fix CVE-2026-43966?
No published fix for CVE-2026-43966 has been found yet. Check the linked vendor advisories for guidance as it becomes available.
Is CVE-2026-43966 being actively exploited?
Not that we know of. CVE-2026-43966 is not in the CISA Known Exploited Vulnerabilities catalog. Its EPSS score of 0.31% is the estimated probability that it will be exploited in the next 30 days. That is higher than 24% of all scored CVEs.
How severe is CVE-2026-43966?
CVE-2026-43966 has a CVSS v4 base score of 6.3, rated low. CVSS rates the technical impact if the vulnerability is exploited, not how likely that is, so weigh it alongside the exploit-prediction score when you decide what to patch first.
Embed a live status badge for CVE-2026-43966
Markdown
[](https://tridentstack.com/cve/CVE-2026-43966)HTML
<a href="https://tridentstack.com/cve/CVE-2026-43966"><img src="https://tridentstack.com/cve/badge/CVE-2026-43966.svg" alt="CVE-2026-43966"></a>Find and fix vulnerabilities across your fleet
TridentStack Control continuously scans your Windows, macOS, and Linux fleet for known vulnerabilities, prioritizes them by severity and active exploitation, and patches them automatically.
This product uses NVD data but is not endorsed or certified by the NVD. EPSS scores courtesy of FIRST.org (https://www.first.org/epss). Source: CISA KEV Catalog. Data as of 2026-07-23.